Mineral oils: processes and products – Chemical conversion of hydrocarbons – Cracking
Patent
1987-04-10
1988-10-25
McFarlane, Anthony
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Cracking
208 48Q, 208 78, 208106, 208132, 585648, 585650, 422193, 422196, 422197, 422200, 422201, C10G 936
Patent
active
047801964
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an improved hydrocarbon steam cracking method intended to produce light olefin, and more particularly ethylene and propylene.
Steam-cracking made its appearance as early as in 1920 to produce ethylene from ethane, and rapidly became a basic method in petrochemistry, using increasingly heavier charges, ranging up to the processing of vacuum gas oils.
Its principle is based on the instability at high temperature of paraffins and naphthenes compared to that of olefin and aromatics. The principal reactions are the scission of a C-C bond by a homolytic rupture mechanism leading to an olefine and a paraffin, and dehydrogenation. These two reactions are endothermic and therefore promoted by a rise in temperature; they also cause an increase in the number of molecules, which means that they are promoted by low partial pressures of the hydrocarbons to be processed. It is for that reason that this pressure is reduced as much as possible by addition of steam to the reaction medium.
However, it was rapidly noticed that maintaining a hydrocarbon charge at a temperature of 800.degree. C. for a time of the order of a few tenths of seconds led to the rapid formation of coke deposits, which is detrimental under several headings: reduction of heat transfer between the reactor and the charge to be cracked, great rise in the temperature of the reactor skin, with reduction of the useful diameter of the reactor causing an increase in the pressure drop inside the reactor, which leads to the shutdown of the unit for a decoking operation.
The formation of coke is due to secondary reactions such as the formation of condensed polycyclic aromatic hydrocarbons, as well as the polymerization of the olefin formed.
This latter reaction stems from the tendency that olefin have to be polymerized when the temperature is of the order of 500.degree.-600.degree. C.; for that reason, in order to reduce the extent of this secondary reaction, the reaction effluents are cooled rapidly (this is often called "quenching") in order to bring them rapidly from the temperature at which pyrolysis takes place to a temperature of below 500.degree. C., generally by means of an indirect heat exchanger.
It was also noticed that the polymerization of the olefin was promoted by the presence of nickel at the surface of the metal walls of the heat exchanger, which acts as a heterogeneous polymerization catalyst (M. DENTE et al., "Fouling of transferline exchanger in ethylene plants", AICHE Meeting at Houston, Tex., 30 Mar. 1983).
Thermodynamic and kinetic studies of hydrocarbon pyrolysis reactions therefore led, in order to increase the selectivity of the reaction towards the production of olefin to act on the following parameters: temperature for a given charge, and maintenance of this temperature as constant as possible in the reaction zone.
From the technology point of view, these imperatives rapidly led to a general method scheme consisting of: limit the residence time of the hydrocarbons during this pyrolysis phase,
Technological development has concentrated essentially on the pyrolysis (b) and quenching phase (c) to attempt to meet the imperatives stated above and the diversity of the charges to be processed, which at present range from ethane to vacuum gas oils.
The developement of the steam-cracking pipe-stills was essentially directed towards obtaining shorter residence times and a reduction in the pressure drop which led manufacturers to reduce the length of pipe-stills, and therefore increase the heat flow density.
The increase of this latter factor can be obtained essentially by increasing the skin temperature of the pipe-stills and/or reducing the diameter of the pipes (which enables the s/v ratio to be increased, s being the exchange surface and v the reaction volume).
The progress made in metallurgy in special alloys resisting increasingly high temperatures (INCOLOY 800H, HK40, HP40 for example) have enabled manufacturers of pyrolysis pipe-stills for steam-cracking to increase the operating tempe
REFERENCES:
patent: 2372186 (1945-03-01), Chaney
patent: 2758061 (1956-08-01), Geller
patent: 3572999 (1971-03-01), Sato
patent: 3579601 (1971-05-01), Kivlen
patent: 3593968 (1971-07-01), Geddes
patent: 3671198 (1972-06-01), Wallace
patent: 3964873 (1976-06-01), Aramaki et al.
patent: 4044068 (1977-08-01), Kurtz
patent: 4097544 (1978-06-01), Hengstebeck
patent: 4150716 (1979-04-01), Ozaki et al.
patent: 4248834 (1981-02-01), Tokumitsu
patent: 4412560 (1983-11-01), Broodman
patent: 4421702 (1983-12-01), Oda et al.
patent: 4457364 (1984-07-01), DiNicolantonio
patent: 4599480 (1986-07-01), Buddell et al.
patent: 4632587 (1986-12-01), Vollhardt
patent: 4683121 (1987-07-01), Goudriaan et al.
Chemical Abstract, 84-129527/21, Mar. 21, 1984.
Chemical Abstract, 84-104040/17, Mar. 15, 1984.
Fouling of Transferline Exchanger in Ethylene Plants, AICHE Meeting, Houston, Tex., Mar. 30, 1983.
New Radiant Coil Technology, Wall et al., Chemical Engineering Progress, pp. 50-55, Dec. 1983.
Ethylene: Keystone to the Petrochemical Industry, Kniel et al., pp. 137-142, 1980.
Alagy Jacques
Busson Christian
Chaverot Pierre
Institut Francais du Pe'trole
McFarlane Anthony
LandOfFree
Hydrocarbon steam cracking method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydrocarbon steam cracking method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydrocarbon steam cracking method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2267746